U.S. patent application number 11/608897 was filed with the patent office on 2007-06-21 for paste coater and pop automatic mounting apparatus employing the same.
This patent application is currently assigned to INTERNATIONAL BUSINESS MACHINES CORPORATION. Invention is credited to Hideo Kimura, Yasuhiko Shiota, Toshiyuki Yokoue.
Application Number | 20070137559 11/608897 |
Document ID | / |
Family ID | 38164952 |
Filed Date | 2007-06-21 |
United States Patent
Application |
20070137559 |
Kind Code |
A1 |
Kimura; Hideo ; et
al. |
June 21, 2007 |
Paste Coater and PoP Automatic Mounting Apparatus Employing the
Same
Abstract
A paste coater that can apply an amount of a solder paste to
small-diameter bump electrodes at a narrow pitch is described. A
paste coater includes: a transfer roller, supported by a sub frame;
a roller drive mechanism for rotating the transfer roller; a paste
storage unit for storing paste to be supplied to the surface of the
transfer roller; a squeegee having a distal edge, parallel to the
rotary shaft of the transfer roller, separated by a gap from the
distal edge to the surface of the transfer roller; a squeegee
holder for holding and including biasing means for pushing the
squeegee in a first direction thereby widening the gap; and a gap
adjustment mechanism with biasing means for pushing the squeegee in
a second direction thereby narrowing the gap.
Inventors: |
Kimura; Hideo; (Shiga,
JP) ; Yokoue; Toshiyuki; (Shiga-ken, JP) ;
Shiota; Yasuhiko; (Shiga-ken, JP) |
Correspondence
Address: |
IBM CORPORATION;ROCHESTER IP LAW DEPT. 917
3605 HIGHWAY 52 NORTH
ROCHESTER
MN
55901-7829
US
|
Assignee: |
INTERNATIONAL BUSINESS MACHINES
CORPORATION
New Orchard Road
Armonk
NY
10504
|
Family ID: |
38164952 |
Appl. No.: |
11/608897 |
Filed: |
December 11, 2006 |
Current U.S.
Class: |
118/256 ;
118/263; 257/E21.508 |
Current CPC
Class: |
H01L 2224/758 20130101;
H05K 3/3485 20200801; H01L 2924/01033 20130101; H01L 2224/13099
20130101; H05K 2201/10734 20130101; H01L 24/11 20130101; H01L
2224/11822 20130101; H01L 2924/01075 20130101; H01L 2924/3025
20130101; H01L 24/75 20130101; H05K 2203/0534 20130101; H01L
2924/01082 20130101; H01L 2924/01005 20130101; H01L 2224/75
20130101; H01L 2924/01015 20130101; H01L 2924/014 20130101; H01L
2924/01013 20130101; H05K 2203/0143 20130101; H01L 2924/01006
20130101; H05K 2201/035 20130101; H01L 2224/136 20130101; H05K
3/1275 20130101; H01L 2224/7515 20130101; H05K 2203/0139 20130101;
H01L 2224/136 20130101; H01L 2924/014 20130101 |
Class at
Publication: |
118/256 ;
118/263 |
International
Class: |
B05C 1/06 20060101
B05C001/06; B05C 11/00 20060101 B05C011/00 |
Foreign Application Data
Date |
Code |
Application Number |
Dec 16, 2005 |
JP |
2005-363827 |
Claims
1. A paste coater for applying solder paste to arrays of bump
electrodes that project outward from a semiconductor package,
comprising: a sub frame; a transfer roller rotatably and
horizontally supported at said sub frame; a roller drive mechanism
for rotating said transfer roller; a paste storage unit for storing
paste to be supplied to the surface of said transfer roller; a
squeegee having a distal edge parallel to a rotary shaft of said
transfer roller, and being located with a gap between the surface
of said transfer roller and the distal edge; a squeegee holder for
supporting said squeegee while urging said squeegee in one of
either a direction to extend the gap or a direction to reduce the
gap; and a gap adjustment mechanism for impelling said squeegee in
the other direction.
2. A paste coater according to claim 1, wherein said squeegee
holder comprises: a leaf spring having one end fixed to said sub
frame and the other end movable, and a movable piece having one end
for supporting said squeegee and the other end fixed to the other
end of said leaf spring; and wherein said gap adjustment mechanism
includes: a screw fitted to said sub frame, and an elevating member
projecting from a head of the screw and contacting said movable
piece.
3. A paste coater according to claim 2, wherein said squeegee is
supported to direct a distal edge to a lower half surface of said
transfer roller, and said paste storage unit is placed on said
squeegee.
4. A paste coater according to claim 3, wherein said roller drive
mechanism comprises: a first side force means for pressing one end
of a rotary shaft of said transfer roller in a direction
perpendicular to the rotary shaft; and a second side force means
for pressing the opposite end of the rotary shaft of said transfer
roller in the opposite direction relative to the direction
perpendicular to the rotary shaft.
5. A paste coater according to claim 4, further comprising: a slide
mechanism for moving said sub frame perpendicular to the rotary
shaft of said transfer roller; and a controller for controlling
said roller drive mechanism and/or said slide mechanism, so that a
tangential velocity at the surface of said transfer roller is lower
than a movement velocity of said sub frame.
6. A paste coater according to claim 5, wherein said controller
operates by controlling the difference between the tangential
velocity at the surface of said transfer roller and the movement
velocity of the sub frame.
7. A package on package automatic mounting apparatus, which mounts
a second semiconductor package supplied with bump electrodes on a
first semiconductor package, comprising: a first tray on which a
plurality of first semiconductor packages are arranged; a second
tray on which a plurality of second semiconductor packages are
arranged; a paste coater for applying solder paste to bump
electrodes on the second semiconductor packages; and package
conveying means for picking up a first semiconductor package from
said first tray and conveying said first semiconductor package to a
predetermined position, for picking up a second semiconductor
package from said second tray and conveying said second
semiconductor package to a paste application position, and for
mounting the second semiconductor package on the first
semiconductor package at the predetermined position after the
solder paste has been applied by said paste coater.
8. A package on package automatic mounting apparatus according to
claim 7, wherein said paste coater comprises: a sub frame; a
transfer roller rotatably and horizontally supported at said sub
frame; a roller drive mechanism for rotating said transfer roller;
a paste storage unit for storing paste to be supplied to the
surface of said transfer roller; a squeegee having a distal edge
parallel to a rotary shaft of said transfer roller, and being
located with a gap between the surface of said transfer roller and
the distal edge; a squeegee holder for supporting said squeegee
while urging said squeegee in one of either a direction to extend
the gap or a direction to reduce the gap; and a gap adjustment
mechanism for impelling said squeegee in the other direction.
9. A package on package automatic mounting apparatus according to
claim 8, wherein said squeegee holder comprises: a leaf spring
having one end fixed to said sub frame and the other end movable,
and a movable piece having one end for supporting said squeegee and
the other end fixed to the other end of said leaf spring; and
wherein said gap adjustment mechanism includes: a screw fitted to
said sub frame, and an elevating member projecting from a head of
the screw and contacting said movable piece.
10. A package on package automatic mounting apparatus according to
claim 9, wherein said squeegee is supported to direct a distal edge
to a lower half surface of said transfer roller, and said paste
storage unit is placed on said squeegee.
11. A package on package automatic mounting apparatus according to
claim 8, wherein said roller drive mechanism comprises: a first
side force means for pressing one end of a rotary shaft of said
transfer roller in a direction perpendicular to the rotary shaft;
and a second side force means for pressing the other end of the
rotary shaft of said transfer roller in the opposite direction
relative to the direction perpendicular to the rotary shaft.
12. A package on package automatic mounting apparatus according to
claim 11, further comprising: a slide mechanism for moving said sub
frame perpendicular to the rotary shaft of said transfer roller;
and a controller for controlling said roller drive mechanism and/or
said slide mechanism, so that a tangential velocity at the surface
of said transfer roller is lower than a movement velocity of said
sub frame.
13. A package on package automatic mounting apparatus according to
claim 12, wherein said package conveying means comprises: a suction
nozzle for holding the second semiconductor package using suction;
and a nozzle conveying means for moving said suction nozzle
perpendicular to the rotary shaft of said transfer roller,
14. A package on package automatic mounting apparatus according to
claim 13, further comprising: a controller for controlling said
roller drive mechanism and/or said nozzle conveying mechanism to
set the tangential velocity of the surface of said transfer roller
lower than the movement velocity of said suction nozzle.
15. A package on package automatic mounting apparatus according to
claim 14, wherein said controller increases or decreases the
velocity differential between the tangential velocity at the
surface of said transfer roller and the movement velocity of the
sub frame.
16. A package on package automatic mounting apparatus according to
claim 12, wherein said package conveying means includes: a first
suction nozzle for holding the first semiconductor package using
suction; a first nozzle conveying unit for conveying said first
suction nozzle to a predetermined position, and for returning said
first suction nozzle to the original position; and a first nozzle
positioning unit for restricting movement of said first suction
nozzle conveyed to the original position by said first nozzle
conveying unit, and for permitting a user to move said first
suction nozzle to a desired position.
17. A package on package automatic mounting apparatus according to
claim 16, wherein said package conveying means further comprises: a
second suction nozzle for holding the second semiconductor package
using suction; a second nozzle conveying unit for conveying said
second suction nozzle to a predetermined position, and for
returning said second suction nozzle to the original position; and
a second nozzle positioning unit for restricting movement of said
second suction nozzle conveyed to the original position by said
second nozzle conveying unit, and for permitting a user to move
said second suction nozzle to a desired position.
Description
FIELD OF THE INVENTION
[0001] The present invention relates to a paste coater and to a PoP
(Package on Package) automatic mounting apparatus that employs the
paste coater. More particularly, the present invention relates to a
paste coater that applies a solder paste to ball electrodes of a
semiconductor package(i.e. ball grid array (BGA)), a chip scale
package and flip chip, and a PoP automatic mounting apparatus that
mounts one semiconductor package atop another.
BACKGROUND OF THE INVENTION
[0002] A semiconductor package, such as a BGA, includes an array of
multiple projecting ball electrodes. In order to mount a
semiconductor package on the obverse face of a printed wiring
board, multiple methods are conventionally utilized such as: a disc
squeegee method, a paste screen print method, or a combination of
the two. These methods generally apply a solder paste to either the
ball electrodes of the semiconductor package or to the wiring
pattern of the printed wiring board.
[0003] The disc squeegee method is a technique whereby a disc
coated with a solder paste is rotated and the solder paste is
smoothed using a squeegee. Thereafter the solder paste is applied
to ball electrodes by dipping them in the solder paste. However,
with this method, it is difficult to adjust or maintain the
rotatory flatness of the rotary disc, and since the rotatory
flatness varies each time the disc is detached, uniform volume of
the transferred solder paste is not available for all the ball
electrodes. This problem is especially seen in warped semiconductor
packages, resulting in non uniform ball electrode heights leading
to coating discrepancies occurring during the spreading of the
solder paste. Another problem occurs when the ball electrodes are
dipped to half their height leading to bridges forming between the
electrodes.
[0004] The paste screen printing method is a technique whereby
screen printing is used to apply solder paste to the wiring pattern
of a printed wiring board before a semiconductor package is
mounted. However, this method is difficult to perform where a
wiring pattern has a pitch of 0.3 mm or smaller. Further, since
this method does not allow for the coating of too much solder
paste, one is unable to absorb the non uniform height of a warped
semiconductor package with excess solder paste. In addition, it is
difficult to utilize this method with a module where an SMC
(Surface Mount Component) is mounted, especially a PoP module that
requires the application of a solder paste to a wiring pattern on a
component mounting side.
[0005] By using a combined method in which both the disc squeegee
and the paste screen printing method are used, the amount of solder
paste applied can be increased, however a increase in costs can not
be avoided.
[0006] In accordance with a reduction in the size and thickness of
a semiconductor package, the pitch of the ball electrodes is
reduced, and the diameter of the ball electrodes becomes minute
(i.e. about 0.4 to 0.2 mm). Therefore, the amount of solder paste
needed for stable application is decreased.
[0007] Further, if a manufacturing variance of .+-.0.1 mm is
present in the heights of ball electrodes, due to the warping of a
semiconductor package, a difference of .+-.0.1 mm will be present
between the center and the peripheral portion. Thus, when too
little solder paste is applied, some of the ball electrodes will
not be coated with solder paste. On the other hand, when too much
solder paste is applied, either bridges will occur between the ball
electrodes, or the solder paste will touch the obverse face of the
board. Therefore, when a conventional method is used to apply
solder paste, the soldered ball electrodes must be inspected,
either visually or using X-ray.
SUMMARY OF THE INVENTION
[0008] One objective of the present invention is to provide a paste
coater that can apply a satisfactory amount of a solder paste to
small-diameter bump (i.e. ball, stud, etc.) electrodes arranged at
small pitches, and a PoP automatic mounting apparatus that employs
this paste coater.
[0009] According to the present invention, a paste coater that
applies solder paste to arrays of bump electrodes, projecting
outward from a semiconductor package, comprises: a sub frame, a
transfer roller, a roller drive mechanism, a paste storage unit, a
squeegee, a squeegee holder and a gap adjustment mechanism. The
transfer roller is rotatably and horizontally supported at the sub
frame. The roller drive mechanism rotates the transfer roller. The
paste storage unit stores paste to be supplied to the surface of
the transfer roller. The squeegee has a distal edge parallel to the
rotary shaft of the transfer roller, and is located with a gap
between the surface of the transfer roller and the distal edge. The
squeegee holder supports the squeegee while urging the squeegee in
one of either a first direction to extend the gap or a second
direction to reduce the gap. The gap adjustment mechanism impels
the squeegee in the other direction.
[0010] Since the gap adjustment mechanism can precisely adjust the
film thickness of the solder paste applied to the transfer roller,
the paste coater can apply a satisfactory amount of solder paste on
small-diameter bump electrodes arranged at a small pitch.
[0011] It is preferable that the paste coater further comprise a
slide mechanism and a controller. The slide mechanism moves the sub
frame perpendicular to the rotary shaft of the transfer roller. The
controller controls the roller drive mechanism and/or the slide
mechanism, so that a tangential velocity at the surface of the
transfer roller is lower than a movement velocity of the sub
frame.
[0012] In this case, since the transfer roller forcibly applies
solder paste to the bump electrodes with shearing motion between
transfer roller and bump electrodes, a large amount of solder paste
is applied to the bump electrodes.
[0013] According to the present invention, a PoP, automatic
mounting apparatus, which mounts a second semiconductor package
supplied with bump electrodes on a first semiconductor package,
comprises: a first tray, a second tray, a paste coater and package
conveying means. A plurality of first semiconductor packages are
arranged on the first tray, while a plurality of second
semiconductor packages are arranged on the second tray. The paste
coater applies solder paste to bump electrodes on the second
semiconductor packages. The package conveying means picks up a
first semiconductor package from the first tray and conveys it to a
predetermined position, picks up a second semiconductor package
from the second tray and conveys it to a paste application
position, and after the solder paste has been applied by the paste
coater, mounts the second semiconductor package on the first at the
predetermined position.
[0014] Since the PoP automatic mounting apparatus applies solder
paste to the bump electrodes of the second semiconductor package
and then mounts the second semiconductor package on the first, the
two semiconductor packages can be efficiently stacked and
packaged.
BRIEF DESCRIPTION OF THE DRAWINGS
[0015] FIG. 1 is a perspective view of the general structure of a
PoP automatic mounting apparatus according to one embodiment of the
present invention;
[0016] FIG. 2 is a front view of a nozzle conveying mechanism used
for the PoP automatic mounting apparatus shown in FIG. 1;
[0017] FIGS. 3A to 3D are shifting diagrams showing the operation
of the nozzle conveying mechanism in FIG. 2;
[0018] FIG. 4 is a front view of a paste coater and is used for the
PoP automatic mounting apparatus in FIG. 1 and a slide mechanism
therefor;
[0019] FIG. 5 is a plan view of the paste coater in FIG. 4 and its
slide mechanism;
[0020] FIG. 6 is a left side view of the paste coater in FIG. 4 and
its slide mechanism;
[0021] FIG. 7 is a partial cross-sectional view taken along line
A-A in FIG. 5; and
[0022] FIG. 8 is an enlarged diagram showing the transfer roller of
the paste coater in FIG. 7 during the application of paste, and a
semiconductor package.
DETAILED DESCRIPTION OF THE INVENTION
[0023] The preferred embodiment of the present invention will now
be described in detail while referring to the drawings. The same
reference numerals are employed to denote identical or
corresponding sections, and an explanation for them will not be
repeated.
PoP Automatic Mounting Apparatus
[0024] While referring to FIG. 1, a PoP automatic mounting
apparatus 10 according to this embodiment mounts a semiconductor
package (i.e. BGA (ball grid arrary), CSP (chip scale packaging) or
a flip chip), atop another semiconductor package, and includes: an
upper tray 11, a lower tray 12, suction nozzles 13-15, nozzle
convey mechanisms 16-18, a position correction unit 19, a paste
coater (including a slide mechanism) 20, an inverting extraction
unit 21, a positioning illumination and vertically identical
viewing camera optical system 22, an alignment color monitor 23 and
a controller 24.
[0025] A plurality of upper semiconductor packages 25 are arranged
on the upper tray 11, and a plurality of lower semiconductor
packages 26 are arranged on the lower tray 12. The suction nozzle
13 picks up one of the semiconductor packages 25 from the upper
tray 11 and holds it by applying suction to its upper face. And the
suction nozzle 14 picks up one of the semiconductor packages 26
from the lower tray 12 and holds it by applying suction to its
upper face.
[0026] The nozzle conveying mechanism 16 moves the suction nozzle
13 to the position correction unit 19, and the nozzle conveying
mechanism 17 moves the suction nozzle 14 to the inverting
extraction unit 21. The nozzle conveying mechanism 18 moves the
suction nozzle 15 from the position correction unit 19 to the
inverting extraction unit 21.
[0027] The position correction unit 19 centers the upper
semiconductor package 25. The position correction unit 19 has an
inverted trapezoidal shaped pocket, and tapered portions used for
positioning are formed in front, at the rear and along the side of
the pocket. The front, rear, and side tapered portions are
independently movable. The paste coater 20 applies a solder paste
to the arrays of ball electrodes on the lower face of the upper
semiconductor package 25.
[0028] The lower semiconductor package 26 is first placed on the
inverting extraction unit 21, and then the upper package
semiconductor package 25 is overlaid. The two packages 25 and 26
are positioned on an aluminum plate and are covered with another
aluminum plate, and the resultant structure is inverted 180
degrees.
[0029] In the operation of the PoP automatic mounting apparatus 10
for stacking two semiconductor packages 25 and 26, the suction
nozzle 13 picks up one upper semiconductor package 25 from the
upper tray 11, and then, the nozzle conveying mechanism 16 moves
the suction nozzle 13 to a location above the position correction
unit 19. Since the suction nozzle 13 releases the upper
semiconductor package 25 at the location above the position
correction unit 19, the upper semiconductor package 25 falls into
the pocket of the position correction unit 19, and as a result, the
upper semiconductor package 25 is centered at a predetermined
location.
[0030] Further, when the suction nozzle 14 picks up one lower
semiconductor package 26 from the lower tray 12, the nozzle
conveying mechanism 17 conveys the suction nozzle 14 to a location
above the inverting extraction unit 21. Then, the suction nozzle 14
releases the lower semiconductor package 26 at the location above
the inverting extraction unit 21, and positions it at a
predetermined location of the inverting extraction unit 21.
[0031] Following this, when the suction nozzle 15 picks up the
upper semiconductor package 25 from the position correction unit 19
again, the nozzle conveying mechanism 18 conveys the suction nozzle
15 to a location above the paste coater 20.
[0032] While the suction nozzle 15 is holding the upper
semiconductor package 25 at the predetermined location above the
paste coater 20, the paste coater 20 applies a solder paste to the
ball electrodes of the upper semiconductor package 25. This process
will be described later in detail.
[0033] After the coater has applied the solder paste, the suction
nozzle 15 moves to a location immediately above the positioning
illumination and vertically identical viewing camera optical system
22, and positions the upper semiconductor package 25 relative to
the lower semiconductor package 26. Thereafter, the suction nozzle
15 descends, and releases the upper semiconductor package 25 above
the inverting extraction unit 21. Thus, the upper semiconductor
package 25 is lying on the lower semiconductor package 26, already
mounted on the inverting extraction unit 21. And as a result, the
upper semiconductor package 25 can be mounted on the lower
semiconductor package 26.
[0034] The nozzle conveying mechanism 16 returns the suction nozzle
13 from the location above the position correction unit 19 to its
original position. Similarly, the nozzle conveying mechanism 17
returns the suction nozzle 14 from the location above the inverting
extraction unit 21 to its original position. At this time, the
suction nozzles 13 and 14 should be positioned at predetermined
locations above the next semiconductor packages 25 and 26 that are
to be selected. This positioning method will now be described by
using the suction nozzle 13 as an example. It should be noted that
the same method is employed for the suction nozzle 14.
[0035] While referring to FIGS. 1 and 2, the suction nozzle 13 is
supported by a nozzle conveying unit 161 that moves along a guide
rail 162. The nozzle conveying unit 161 rotatably supports a lever
163, which rotatably holds a roller 164 at its distal end. The
lever 163 is urged upright, for example, by a spring, when a nozzle
positioning unit 165 releases the nozzle conveying unit 161, i.e.,
the suction nozzle 13 (see FIG. 3(a)). The lever 163 is horizontal
when the nozzle positioning unit 165 locks the nozzle conveying
unit 161 (see FIG. 3(d)).
[0036] The nozzle positioning unit 165 includes a guide groove 166
formed to guide a roller 164 for the nozzle conveying unit 161. The
guide groove 166 is formed vertically, and has an opening 167,
formed in a side wall, for accepting the roller 164. The nozzle
positioning unit 165 is manually movable in the X direction by a
rack and pinion mechanism 168.
[0037] When the nozzle positioning unit 165 has been manually moved
and fixed at a desired position, the nozzle conveying unit 161
returns and its roller 164 enters the opening 167 of the nozzle
opening unit 165 (see FIG. 3(b)). And while the nozzle conveying
unit 161 is sequentially moving, the roller 164 descends along the
guide groove 166 and the lever 163 pivots and inclines (see FIG.
3(c)). After the lever 163 has pivoted 90 degrees and becomes
horizontal (see FIG. 9D), the nozzle conveying unit 161 is driven
against the positioning unit 165 in the direction of movement, and
is positioned.
[0038] Then, adjustment knobs 27 and 28 are manually turned to move
the upper tray 11 in the XY direction, so that the suction nozzle
13 reaches a predetermined position above the next semiconductor
package 25 that is to be picked up. When the nozzle positioning
unit 165 that currently is holding the nozzle conveying unit 161 is
manually moved, the nozzle conveying unit 161 also moves, and the
positioning of the suction nozzle 13 can be manually changed.
[0039] Though the PoP, automatic mounting apparatus automatically
conveys the suction nozzles 13 and 14 to the positions for mounting
the semiconductor packages 25 and 26 is automated, the PoP mounting
apparatus permits a user to manually convey the suction nozzles 13
and 14 to the positions to pick up the semiconductor packages 25
and 26, the user does not need to enter in advance positions
(coordinate data) for picking up the semiconductor packages 25 and
26, or to change a control program for each type of semiconductor
package.
Paste Coater
[0040] While referring to FIG. 4-FIG. 7, the paste coater 20
includes a sub frame 30, a transfer roller 32, a roller drive
mechanism 34, a paste storage unit 36, a squeegee 38, a squeegee
holder 40 and a gap adjustment mechanism 42.
[0041] The transfer roller 32 is horizontally held in the sub frame
30 and is rotatable. In order for the transfer roller 32 to be
rotated in a direction indicated by an arrow in FIG. 7, the roller
drive mechanism 34 includes: a motor 44 fitted with a gear head; a
drive pulley 46 fixed to the drive shaft of the motor 44; a drive
pulley 48 fixed to one side of the transfer roller 32; and a power
transmission belt 50 extended between the drive pulleys 46 and
48.
[0042] An idler pulley 52 is fixed to the other side of the
transfer roller 32, and below this, another idler pulley 54 is
rotatably held in the sub frame 30 and a power transmission belt 56
is extended between the idler pulleys 52 and 54. The drive pulleys
48 and 46 and the power transmission belt 50 pull and press one end
of the rotary shaft of the transfer roller 32 downward
perpendicular to the rotary shaft, and the idler pulleys 52 and 54
and the power transmission belt 56 also pull and press the other
end of the rotary shaft downward. This process prevents the
transfer roller 32 from microscopic wobbling which cause
inhomogeneous film thickness of solder.
[0043] The paste storage unit 36 stores solder paste to be supplied
to the surface of the transfer roller 32. In order to prevent the
spreading and leaking of the a solder paste, the paste storage unit
36 includes a paste stop guide 58 that is almost U-shaped in plan
view and that is secured to the top of the squeegee 38 by bolts.
The inner wall of the paste stop guide 58 is tapered toward the
transfer roller 32, so that all the solder paste can flow toward
the transfer roller 32.
[0044] The distal edge of the squeegee 38 is located parallel to
the rotary shaft of the transfer roller 32, and separated by a gap
from the surface of the transfer roller 32, so as to maintain a
constant film thickness for the solder paste attached on the
surface of the transfer roller 32.
[0045] The squeegee holder 40 includes: a fixed piece 60 secured to
the sub frame 30; a movable piece 62 almost L-shaped in cross
section; and a bent leaf spring 64 almost U-shaped in cross
section. With this arrangement, the squeegee holder 40 pushes the
squeegee 38 in a direction (downward) that widens the gap defined
between the surface of the transfer roller 32 and the distal edge
of the squeegee 38. The paste storage unit 36 and the squeegee 38
are mounted on the distal end of the movable piece 62. One side of
the leaf spring 64 is fixed to the fixing piece 60 by a bolt, and
the other side is fixed to the movable piece 62 by a bolt.
Therefore, the movable piece 62 serves as a cantilever, employing
the leaf spring 64 as a fulcrum, and its the distal end is urged
downward.
[0046] The gap adjustment mechanism 42 includes: an adjustment
screw 66 fitted in the sub frame 30; and an elevating member 68,
projected upward from the head of the adjustment screw 66. With
this arrangement, the gap adjustment mechanism 42 pushes the
squeegee 38 in a direction that reduces the gap between the surface
of the transfer roller 32 and the distal edge of the squeegee 38.
When the adjustment screw 66 is loosened, the elevating member 68
pushes the movable piece 62 up and the gap between the surface of
the transfer roller 32 and the distal edge of the squeegee 38 is
narrowed. And when the adjustment screw 66 is tightened, the
elevating member 68 descends, the movable piece 62 follows due to
the biasing force of the leaf spring 64, and the gap between the
surface of the transfer roller 32 and the distal edge of the
squeegee 38 is widened.
Slide Mechanism for Paste Coater
[0047] A slide mechanism 29 for the paste coater 20 includes: a
fixed base plate 70; two linear guide rails 72 laid on the fixed
base plate 70; a moving base plate 74 slidable along the linear
guide rails 72; and a base plate drive mechanism 76 that slides the
moving base plate 74. The paste coater 20 is mounted on the moving
base plate 74.
[0048] The base plate drive mechanism 76 includes: a stepping motor
78, mounted on the moving base plate 74 with the paste coater 20; a
winding drum 80 fixed to the drive shaft of the stepping motor 78;
a traction wire 82 extended above the fixed base plate 70; and an
end detection unit (88R, 88L and 90) for detecting the distance the
moving base plate 74 has slid and whether if has reached either
end.
[0049] The traction wire 82 is extended along the linear guide
rails 72 and is wound around the winding drum 80 several times in
the middle, and is fixed at its ends to a wire extension fitting 86
standing upright on the fixed base plate 70.
[0050] When the stepping motor 78 rotates the winding drum 80
clockwise (from the top to the bottom in FIG. 4) and winds in the
right portion of the traction wire 82 (in FIG. 4 or 5), the moving
base plate 74 and the paste coater 20 mounted on the moving base
plate 74 move to the right (while referring to FIG. 4 or 5). On the
other hand, when the stepping motor 78 rotates the winding drum 80
counterclockwise (from the bottom to the top in FIG. 4) and winds
in the left portion of the traction wire 82 (in FIG. 4 or 5), the
moving base plate 74 and the paste coater 20 mounted on the moving
base plate 74 move to the left (while referring to FIG. 4 or
5).
[0051] The end detection unit includes: optical sensors 88R and
88L, such as photointerrupters, and a light blocking plate 90 to be
inserted into or removed from the gap between the optical sensors
88R and 88L. The optical sensors 88R and 88L are secured to the
respective ends of a sensor mounting fixture 92 provided upright on
the fixed base plate 70. The light blocking plate 90 is integrally
formed with a motor mounting fixture 94 to attach a motor 44.
[0052] When the moving base plate 74 has moved to the left end (in
FIG. 4 or 5), the light blocking plate 90 enters the gap of the
optical sensor 88L and blocks light, and the optical sensor 88L
detects that the moving base plate 78 detects that the moving base
plate 74 has reached the left end. On the other hand, when the
moving base plate 74 has moved to the right end (in FIG. 4 or 5),
the light blocking plate 90 enters the gap of the optical sensor
88R and blocks light, and the optical sensor 88R detects that the
moving base plate 84 detects that the moving base plate 74 has
reached the right end.
[0053] When the suction nozzle 15 holds the semiconductor package
25 at a predetermined position above the paste coater 20, the
controller 24 permits the roller drive mechanism 34 and the slide
mechanism 29 to rotate the transfer roller 32 and move the paste
coater 20. At this time, as shown in FIG. 8, the tangential
velocity Vr at the surface of the transfer roller 32 is lower than
the movement velocity Vx of the sub frame 30 (i.e., the transfer
roller 32).
[0054] In this embodiment, the controller 24 controls both the
roller drive mechanism 34 and the slide mechanism 29. However, the
controller 24 may control only the slide mechanism 29 while the
transfer roller 32 continues to rotate at a constant speed, or may
control only the roller drive mechanism 34 while the paste coater
20 continues to move at a constant speed.
[0055] Since the tangential velocity Vr of the transfer roller 32
is not equal, but is slightly lower than the movement speed Vx of
the transfer roller 32, a solder paste P can be applied to ball
electrodes 251 by shearing motion between transfer roller and bump
electrodes, and a considerably large amount of the solder paste P
can be retained downstream and be used for application to the ball
electrodes 251.
[0056] It is preferable that the diameter of the transfer roller 32
be about 2 to 20 times the pitch of the ball diameter 251. In this
case, several of the arrays (specifically, about three to eight
arrays) of the ball electrodes 251 are dipped in the solder paste P
attached to the transfer roller 32. The preferable film thickness
of the solder paste P on the transfer roller 32 is about 0.2 mm.
For precise adjustment of this film thickness, a user need only
manually turn the adjustment screw 66 and change the gap between
the surface of the transfer roller 32 and the distal edge of the
squeegee 38.
[0057] Furthermore, for the adjustment of the amount of the solder
paste P to be applied to the ball electrodes 251, the user need
only change the velocity differential between the tangential
velocity Vr of the transfer roller 32 and the movement velocity Vx
of the transfer roller 32, or control the height of the suction
nozzle 15 (i.e., the depth of dipping the ball electrodes 251).
Specifically, bridges will not occur by dipping up to two thirds of
the depth of the ball electrodes 251.
[0058] A change in the amount of coating is also adjustable by
optimizing an application condition as the velocity Vr.apprxeq.Vx
is changed within a range of 10 to 100 mm/second in accordance with
physical property differences, such as the viscosity of a solder
paste, thixotropic ratio, a mixture ratio of a solder ball to a
flux element and a mixture ratio of solder balls having different
particle sizes. As synergism, the attachment of a solder paste to
the surface of a board and the formation of a bridge are prevented.
Generally, as the velocity increases, the bridge prevention effects
become greater.
[0059] When the pitch of the ball electrodes 251 is near the
diameter of the transfer roller 32, the transfer roller 32 would
fit between two adjacent arrays of the ball electrodes 251. To
avoid this, the semiconductor package 25 may be moved so as to
position the arrays of the ball electrodes 251 obliquely, relative
to the transfer roller 32.
[0060] A flexible material, such as sponge, may be used for the
surface of the transfer roller 32 to absorb the height difference
of the ball electrodes 251 and to stably apply an appropriate
amount of solder paste.
[0061] Instead of moving the paste coater 20 in the above
embodiment, the suction nozzle 15 (i.e., the semiconductor package
25) may be moved. In this case, the nozzle conveying mechanism 18
moves the suction nozzle 15 perpendicular to the rotary shaft of
the transfer roller 32. The controller 24 controls the roller drive
mechanism 34 and the nozzle conveying mechanism 18 so as to set the
tangential velocity Vr at the surface of the transfer roller 32
lower than the movement velocity Vx of the suction nozzle 15. In
this example, the controller 24 controls both the roller drive
mechanism 34 and the nozzle conveying mechanism 18; however, as
previously described, the controller 24 may control either one of
them.
[0062] Both the paste coater 20 and the suction nozzle 15 may be
moved. The controller 24 controls the roller drive mechanism 34,
the slide mechanism 29 and the nozzle conveying mechanism 18. In
short, the controller need only set the movement velocity Vx of the
transfer roller 32, relative to the semiconductor package 25,
higher than the tangential velocity Vr of the transfer roller
32.
[0063] In the above embodiment, the squeegee 38 and the paste
storage unit 36 each include two members. However, a squeegee and a
storage unit may be integrally provided by forming, in the
squeegee, a recessed portion that serves as a storage unit.
[0064] The embodiment of the present invention has been described.
However, this embodiment is merely an example for carrying out the
present invention, and the present invention is not limited to this
embodiment and can be provided by variously modifying the
embodiment without departing from the subject of the invention.
* * * * *